DIY C-41 Potassium Iodide

[Adrian Bacon]

Hi everyone!

I'm new to APUG, but a really, really long time lurker.

I generally do my C-41 with the Unicolor powder press kit, but have decided to try my hand at some DIY and this has lead me to some questions that I could not readily find a thread here for an answer (at least not an obvious thread), so here goes:

I've found several recipes for the developer here on APUG and noticed that some of them prescribe potassium iodide and some don't. When prescribed, it's such a tiny amount that I think I'd have trouble measuring that out reliably, though saw a post in a thread that described a way to do it, but ended up with leftover.

My question: what does the potassium iodide do and can I get away without it by compensating with one of the other ingredients or just simply not include it? I've been looking at the MSDS of other press kits and haven't seen it there FWIW.

Many thanks in advance, also, Photo Engineer: Sir, you rock. You have happily provided invaluable amounts information here on APUG. As a lurker, when searching through the archives for information I inevitably find myself looking to see if you chimed in and what you say (not saying the other posters don't add value because they do). APUG is a veritable goldmine of info, I should have joined in years ago.

 

[sfaber17]

Most formulas make use of it. Haven't tried the ones without it yet. It acts as a restrainer for blue in particular I believe. The blue layer is the outermost layer. It has a tendency to be a bit too dense in most of these formulations, especially for Fuji film, and the iodide helps keep it under control. Agitation can affect the blue layer density also, more so than the others.

 

[sfaber17]

As far as measuring it out, I would make a liter of it with 1.00 gram if you have such a scale. Then use a 1ml pipet from there to measure out to the nearest .01 ml.
I have an analytical balance, so I pick a small crystal and weigh it - say 86 mg, and dissolve it in 86 ml of water for the same result.

 

[Photo Engineer]

KI solution will only keep for about 1 - 6 months depending on storage conditions.

In addition to the above antifoggant effects, it tends to balance out the edge effects and color correction, and also allows the developer to work better in a continuous seasoned process.

The amount added allows a fresh developer to mimic a seasoned one within limits.

PE

 

[Adrian Bacon]

Ahh. (Light bulb moment). My primary CN is Ektar 100 and my only real complaint with it is that the blue channel is nearly overwhelmingly dense when scanning it (yes, I'm one of those "evil hybrids"). This explains a lot.

I'm definitely going to include that into my soup.

I can't really safely do storage of mixed chemistry (kids and family), so my usual mode of operation is to keep the dry ingredients up high in a locked toolbox out in the garage, hold my film until I have enough to do a run, then spend an evening after the kids are down for the night doing it with disposal afterwards. For that purpose, the press kit works, however now I'm thinking I can do better and end up with an easier to scan negative. Looks like I'll be investing in a better scale.

Thank you!

If you guys want, I'll post another thread with the soup I ended up with and the results. I plan to burn some 4x5 with a reflected black, 18% gray, and white along with a whibal and colorchecker during noon time as a test. It'll be at least a couple weeks down the road as I still need to assemble the chemistry.

 

[OptiKen]

Ahh. (Light bulb moment).
If you guys want, I'll post another thread with the soup I ended up with and the results. I plan to burn some 4x5 with a reflected black, 18% gray, and white along with a whibal and colorchecker during noon time as a test. It'll be at least a couple weeks down the road as I still need to assemble the chemistry.

I would definitely be interested in seeing both your formula and your results

 

[darkroommike]

As has been said by others, it's a very powerful restrainer, mix up a little bit as a percentage solution and then take up the little you need with a pipette. Potassium iodide has other darkroom applications including SLIMT but a little bit goes a long way so don't buy 500 grams of it.

 

[Murray Kelly]

KI solution will only keep for about 1 - 6 months depending on storage conditions.

In addition to the above antifoggant effects, it tends to balance out the edge effects and color correction, and also allows the developer to work better in a continuous seasoned process.

The amount added allows a fresh developer to mimic a seasoned one within limits.

PE

Does KI dissolve in other solvents - eg glycerol or glycol or acetone? Or perhaps alcohol? Its life might be more useful kept that way.

 

[Photo Engineer]

Not that I am aware of. It is a fully ionic salt for all practical purposes. It also goes bad dry in bottles due to oxidation forming iodates.

PE

 

[Murray Kelly]

Not that I am aware of. It is a fully ionic salt for all practical purposes. It also goes bad dry in bottles due to oxidation forming iodates.

PE

TU once more!
I am checking out Povidone -iodine (Betadine) prep solution in alcohol. Could be a long life solution (pun). Question is; quantum. ?? 6mg/minim?? A drop @ 16 / ml.
Some are using Betatdine as a C41 bleach. Can't see the advantage over the myriad alternatives.

 

[Photo Engineer]

Betadine in developer will be an unknown. Some activity can come from the poly vinyl pyrolidone itself perhaps.

PE

 

[Chris Livsey]

Soluble in Glycerol 1 in 2 and alcohol (Ethanol) 1 in 22 (water 1 in 0.7)

 

[Photo Engineer]

Yes, and 2 g/100 ml of alcohol and 1.3 g/ 100 ml of acetone. I would not use any of these in photo solutions with KI due to decomposition and reactivity.

I make a 1% solution and use it for 1 - 2 months then toss it. That way, a 100 g bottle can last me 200 months under most conditions.

Due to formation of periodates, it can give unpredictable results when used from organic solvents.

PE

 

[Rudeofus]

If you have a 1% solution of KI, keep it for a long time, and some part of the KI would convert to KIO3: would that KIO3 go back to KI state when you add it to color developer? Given the minuscule amounts of KI needed in typical color developers, the loss of developer caused by adding KIO3 instead of KI would be negligible, yes?

 

[Photo Engineer]

But the amount if KI is critical and it would become a variable this way.

PE

 

[Rudeofus]

But the amount if KI is critical and it would become a variable this way.

Nope, that wouldn't change, as long as we start with 1% solution and not with powder compound. Neither K+, nor I-/IO3- produce any volatile compounds in the process, therefore we should end up with a very predictable amount of KI in the developer.

 

[sfaber17]

I think the point was if IO3 - doesn't act or revert to I- then it would be unpredictable.

 

[Rudeofus]

I think the point was if IO3 - doesn't act or revert to I- then it would be unpredictable.

I believe that color developer will reduce any IO3 - back to I - at once. If this wasn't the case, C-41 CD would have terrible shelf life, both as working solution and as a concentrate, and the same would be true for E6 FD and E6 CD.

 

[Photo Engineer]

If this reaction were possible, then the developer would cycle indefinitely until all of the CD and Oxygen is used up. There are both Iodates and Periodates that are possible in this mix. That is why it is so simple to just use KI.

PE

 

[Rudeofus]

If this reaction were possible, then the developer would cycle indefinitely until all of the CD and Oxygen is used up. There are both Iodates and Periodates that are possible in this mix. That is why it is so simple to just use KI.

Commercially available C-41 kit concentrates contain substantially less than 1% KI. These concentrates would not last for a year if the KI wouldn't be restored by CD agent. And yes, the CD-4 will be used up quickly if you let enough Oxygen near it.

 

[falotico]

Obviously there is a difference between adding KI solution and additing KI + KIO3. If the developer has to reduce KIO3 to KI then you suffer a loss of reduction potential in the developer.

 

[Photo Engineer]

There are two points in my post above. One is that the KI is the critical ingredient here and it can vary if you rely on a redox situation, and the second is that under those conditions, you will never know how much KI is present.

PE

 

[Murray Kelly]

So, not knowing the rate of degradation of the crystalline KI, would it be reasonable to dissolve it as a concentrate and store it with argon (from a wine shop) above it to stop the oxygen ruining the little you need but can't ordinarily keep otherwise?

 

[sfaber17]

Maybe adding a bit of sulfite to our stock KI solution would be a good idea. I know with chlorine analogs, the more oxidized you get - hypochlorite -> chlorate -> perchlorate, the more stable the salt is. It is likely the case for iodine. Mix sulfur with hypochlorite and it will ignite itself, mix with chlorate and it is dangerous, mix with perchlorate and no problem until a train runs over it.

 

[Murray Kelly]

What I am about to ask is a bit left field and I apologise to the OP for this. The periodic table lists chloride, bromide, iodide and fluoride.
Each seems to be 1000x more active than the previous one in the chemistry we are talking about. Is fluoride effective in nanograms for the purpose of reducing fog?
I retreat to the bunker with my non-fluoridated tap water.